/* scanner for a toy Pascal-like language */

         %{
         /* need this for the call to atof() below */
         #include <math.h>
         %}

         DIGIT    [0-9]
         ID       [a-z][a-z0-9]*

         %%

         {DIGIT}+    {
                     printf( "An integer: %s (%d)\n", yytext,
                             atoi( yytext ) );
                     }

         {DIGIT}+"."{DIGIT}*        {
                     printf( "A float: %s (%g)\n", yytext,
                             atof( yytext ) );
                     }

         if|then|begin|end|procedure|function        {
                     printf( "A keyword: %s\n", yytext );
                     }

         {ID}        printf( "An identifier: %s\n", yytext );

         "+"|"-"|"*"|"/"   printf( "An operator: %s\n", yytext );

         "{"[\^{}}\n]*"}"     /* eat up one-line comments */

         [ \t\n]+          /* eat up whitespace */

         .           printf( "Unrecognized character: %s\n", yytext );

         %%

         int main( int argc, char **argv )
             {
             ++argv, --argc;  /* skip over program name */
             if ( argc > 0 )
                     yyin = fopen( argv[0], "r" );
             else
                     yyin = stdin;

             yylex();
        }

